In recent years, ethanol has attracted attention as a fuel source alternative to petroleum fuels. However, for adopting ethanol as a fuel, it is necessary to purify, by distillation, a crude product obtained from a biomass such as corn, and then to perform dehydration until at least 99.5 wt % is reached.
Known conventional dehydration methods include a method for separating water from the treated fluid by the pervaporation method (penetrative vaporization (PV) method) using a water separation membrane (see, for example, Patent Literature 1). In the dehydrator discussed by Patent Literature 1, a plurality of columnar water separation membranes is arranged inside a shell part in series. Each water separation membrane is provided with a plurality of flow paths, each of which having a predetermined diameter. In the water separation membrane described above, the treated fluid simultaneously flows through all the flow paths at a predetermined velocity and water is separated from the treated fluid while the treated fluid flows through the flow paths.